Combined steering and braking means for crawler tractor

ABSTRACT

A crawler tractor has an engine-driven fluid power shifted transmission for supplying motive power to left and right crawler tracks through spring-applied fluid-released left and right steering clutches and also has spring-applied fluid-released brake actuators for the track brakes. A hydraulic control system for steering and braking the tractor includes a combined steering and braking valve having a pair of lever operated valve spools, a shuttle valve, and a supplemental brake control valve operated by a single brake pedal. The combined steering and braking valve, which includes a flow divider, directs fluid from a pump to the brake actuators to maintain the brakes released when the valve spools are in neutral. When a lever operated valve spool is moved from neutral to some other position, the combined steering and braking valve directs fluid to disengage a clutch and causes the brake for the associated track to be applied. The combined steering and braking valve operates to regulate fluid pressure in the system and also operates to ensure that sufficient fluid pressure is available for clutch operation regardless of brake actuator demands. The shuttle valve is connected to the brake actuators and is responsive to the supplemental brake valve to apply either or both brakes when the supplemental brake valve is actuated either by the brake pedal or in response to a drop of fluid pressure in the power shift transmission.

This is a division, of application Ser. No. 640,767, filed Dec. 15,1975, now U.S. Pat. No. 4,037,677.

BACKGROUND OF THE INVENTION

1. Field of Use

This invention relates generally to combined steering and braking meansfor a crawler tractor or the like. In particular, it relates to ahydraulic control system having a combined steering and braking valvetherein as well as other components.

2. Description of the Prior Art

In some prior art crawler tractors the hydraulic control system for thesteering clutches and the track brakes includes a pair of manuallyoperated steering clutch levers which actuate the valves for thesteering clutches which transmit motive power from the tractortransmission to the tracks. A pair of brake pedals are used toselectively actuate a pair of brake cylinders which, in turn, control apair of brakes for the tracks. Straight line vehicle movement isaccomplished by engaging both clutches so as to drive both tracks in thesame direction at the same speed. Steering is accomplished by operatingone steering clutch lever so as to disengage its associated steeringclutch and thereby slow down or stop its associated track whilecontinuing to drive the other. Braking is accomplished during straightline vehicle movement by using both brake pedals and, during steering,by using the brake pedal for that track whose clutch is disengaged.

In such prior art tractors the steering clutches and the brake actuatorsare sometimes embodied in separate control systems which are suppliedfrom separate hydraulic pumps. Aside from increased costs of suchsystems resulting from redundancy of components, such prior art systemsoften lack various automatic control functions which, if provided, wouldsimplify and provide for safer tractor operation. The following U.S.Pat. Nos. disclose various types of prior art steering and brakingcontrol systems for vehicles: 3,437,184; 3,358,786; 3,386,523;3,351,149; and 2,375,959.

SUMMARY OF THE INVENTION

A crawler tractor has an engine-driven fluid power shifted transmissionfor supplying motive power to left and right crawler tracks throughspring-applied fluid-released left and right steering clutches and alsohas spring-applied fluid-released brake actuators for the track brakes.A hydraulic control system for steering and braking the tractor includesa combined steering and braking valve having a pair of lever operatedvalve spools, a shuttle valve, and a supplemental brake control valveoperated by a single brake pedal. The combined steering and brakingvalve, which includes a flow divider, directs fluid from a pump to thebrake actuators to maintain the brakes released when the valve spoolsare in neutral. When a lever operated valve spool is moved from neutralto some other position, the combined steering and braking valve directsfluid to disengage a clutch and causes the brake for the associatedtrack to be applied. The combined steering and braking valve operates toregulate fluid pressure in the system and also operates to ensure thatsufficient fluid pressure is available for clutch operation regardlessof brake actuator demands. The shuttle valve is connected to the brakeactuators and is responsive to the supplemental brake valve to applyeither or both brakes when the supplemental brake valve is actuatedeither by the brake pedal or in response to a drop of fluid pressure inthe power shift transmission. If both levers are in neutral andtransmission fluid pressure drops below a predetermined value, as duringreverse shifting to change direction of tractor travel, the supplementalvalve effects automatic spring application of both brakes.

A control system having combined steering and braking valve inaccordance with the invention require fewer duplicate components thanprior art systems, is easier to operate and more reliable in operation.The system provides for a single brake pedal usable for steering andbraking. The system employs fail-safe spring-applied brakes, requiresonly one pump for supplying the steering clutches and brake actuators,and enables automatic braking when the steering levers are in neutraland transmission fluid pressure drops, as during tractor directionreversal. The system employs an improved yet relatively uncomplicatedpedal operated supplemental brake valve to enable selective as well asautomatic braking. Other objects and advantages will hereinafter appear.

DRAWINGS

FIG. 1 is a schematic diagram of a control system in accordance with theinvention;

FIG. 2 is a top elevation view of a combined steering-brake valve shownin FIG. 1;

FIG. 3 is a side elevation view of the valve of FIG. 2;

FIG. 4 is a cross section view of the valve taken on line 4--4 of FIG.3;

FIG. 5 is a cross section view of the valve taken on line 5--5 of FIG.4;

FIG. 6 is a cross section view of the valve taken on line 6--6 of FIG.4;

FIG. 7 is a cross section view of the valve taken on line 7--7 of FIG.4; and

FIG. 8 is a schematic diagram of the steering-brake valve.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIG. 1, a crawler tractor has left and right crawler tracks1 and 2, respectively, on opposite lateral sides thereof, an engine 3for driving a transmission 4 to supply motive power to the tracksthrough conventional spring-applied fluid-released left and rightsteering clutches 5 and 6, a conventional spring-applied fluid-releasedleft and right brakes 7 and 8, respectively, which are actuated by leftand right brake actuators 9 and 10, respectively. The tractor alsocomprises manually operable left and right steering clutch and brakecontrol levers 31 and 32 and a single brake pedal 33.

Transmission 4 is a power shift transmission for driving the tractor andhas an output shaft 11 which extends into a housing 12 to drive a mainshaft 13 through bevel gears 14. Main shaft 13 is connectable throughthe clutches 5, 6 when the latter are engaged to drive the left andright final drive shafts 15 and 16, respectively, to which track drivesprockets 17 and 18, respectively, are affixed.

Each brake 7, 8 comprises a brake drum 20 for the final drive shaft 15,16 and a brake band 21 engageable with the brake drum. Each brakeactuator 9, 10 comprises a housing 22 having a piston 23 therein formoving a piston rod 24 attached thereto which extends from the housing.Each housing 22 is rigidly secured to the tractor frame by means notshown. Each piston rod 24 is connected by a linkage 26 to an associatedbrake band 21. Each brake actuator 9, 10 comprises biasing spring meansin the form of a pair of balanced compression springs 27 and 28 withinits housing 22 for biasing the piston 23 in one direction to a positiontoward one end of the housing wherein brake bank 21 fully engages itsbrake drum 20 and the brake 7, 8 is applied. Each housing 22 furthercomprises a fluid inlet port 30 for admitting fluid between the piston23 and the said one end of the housing to effect piston movement in theopposite direction to release the brake 7, 8. The actuators 9 and 10 aremechanically connected to the brakes 7 and 8, respectively, and arespring biased to effect engagement of the brakes when the fluid pressurein the actuators 9 and 10, respectively, drops below a predeterminedvalue.

The control system for steering and braking includes a singleengine-driven pump 40 for supplying fluid to operate the steeringclutches 5, 6 and the brake actuators 9. 10; a combined steering andbraking valve 41 responsive to actuation of the levers 31, 32 to supplyfluid to release the steering clutches 5, 6 and to release the brakes 7,8; a shuttle valve 42 responsive to operation of the steering clutches5, 6 to cause the brake actuators 9, 10 to effect brake application, anda supplemental brake control valve 43 operated by a pedal 33 and alsoresponsive to transmission fluid pressure.

Generally speaking, the control system operates in such a manner thatactuation of either lever 31, 32 effects fluid release of its associatedsteering clutch 5, 6 and application of the appropriate brake 7, 8.Operation of the single brake pedal 33 will also effect springapplication of the brake 7, 8 for that track 1, 2 whose clutch 5, 6 isreleased. If both levers 31, 32 are in neutral and transmission fluidpressure drops below a predetermined value, as during reverse shiftingto change direction of tractor travel, both brakes 7, 8 areautomatically spring-applied. Functions for both situations occurwithout loss of fluid pressure necessary for control of the steeringclutches 5, 6 because of a pressure regulating sequence in valve 41. Ifboth levers 31, 32 are in neutral with both steering clutches 5, 6engaged, operation of the single brake pedal 33 will then effect springapplication of both brakes 7, 8 such as may be desirable during downhill coast.

Valve 41, which is understood to have a flow divider 46 therein, has afluid inlet port 50 connected to pump 40 by a fluid line 51, an outletport G connected to a reservoir 112 by a line 124, and also has clutchsupply or pressure ports C and D which are connected by fluid lines 55and 56, respectively, to the clutches 5 and 6, respectively. Valve 41also has brake supply or pressure ports F and E for supplying the fluidports 30 of the brake actuators 9 and 10, respectively, through lines 89and 90, respectively. The lines 89 and 90 are connected by lines 83 and84, respectively, to the ports 81 and 82, respectively, of shuttle valve42. Valve 41 is provided with a housing 200 and with left and rightvalve spools 211 and 217, slideable in bores 201 and 202, respectively,which are connected for actuation by the levers 31 and 32, respectively.The spools 211 and 217 are normally biased in neutral position whereinthey prevent fluid flow from pump 40 to the steering clutches 5 and 6 tomaintain the clutches spring-engaged but permit flow to the brakeactuators 9 and 10 to maintain the brakes 7 and 8 released. The spoolsare axially movable therefrom by the levers 31 and 32 to effect fluidflow from pump 40 to release the clutches 5 and 6, respectively, and toprevent fluid flow to the actuators 9 and 10 to apply the brakes 7 and8, respectively. To ensure engagement of clutches 5 and 6 when valvespools 211 and 217 are in neutral position, bleed-down restrictororifices 124 and 125 are provided to allow pressure fluid in lines 55and 56 to escape to reservoir 112A. Valve 41 is hereinafter described indetail.

In addition to steering clutch and brake control, the valve 41 alsoprovides pressure regulation sequence and pressure control valving.Referring to FIGS. 1, 4, and 8, valve 41 comprises a housing 200. Fluidfrom the flow divider 46 entering a main inlet port A passes into achamber 210 that is associated with spool 211. In the neutral positionof the valve spool 211, an opening 212 is available for the fluid toenter from chamber 210 into another chamber 213, then through a passage214 and a check valve 215 to a chamber 216 associated with the othervalve spool 217. Fluid in chamber 216 is available at pressure port Ewith pressure to apply against the spring 27 in the right hand brakecylinder 10 to release the right hand spring applied brake 8 (shown inFIG. 1). Fluid pressure is regulated by first pressure regulating meansincluding a sleeve 218 surrounding spool 217 and slideable within thespool bore 202 in the valve housing 200. A spring 219 reacting axiallyagainst a washer 220 on spool 217 forces sleeve 218 upward tending toclose an annular passage 221 between chamber 216 and chamber 222. Thecombination of spring 219 force and the cross sectional area at theupper end of sleeve 218 tending to close passage 221 establishes thefluid pressure applied at port E to release the right hand brake 7. Thereaction force axially applied downwardly on spool 217 by spring 219 isamply resisted by a spring 223 located at the upper end of spool 217 andbiasing the spool upward against a stop 224. The fluid in chamber 222 isreturned to tank through pressure port G.

Similarly, fluid from the flow divider 46 entering a main outlet port Bprogresses in like manner with relation to like components to providepressure at pressure port F for releasing the left hand brake 8.

In order to release (disengage) the normally spring-applied steeringclutches 5, 6, either or both valve spools 211 and 217 are manuallymoved downwardly (in FIGS. 1, 2, 3, 4, 5, and 8) against the force ofspring 223 of spool 217 and spring 223a of spool 211.

A vehicle turn to the right is accomplished by pulling on the right handsteering lever 32 to shift valve spool 217 away from stop 224 againstthe force of spring 223. Fluid pressure supplied by the flow divider 46at main inlet port B from the hydraulic pump 40 passes through chamber210a, to chamber 225, out pressure port D to the right hand steeringclutch 6 thereby releasing it.

Supplemental pressure regulation is provided by second pressureregulating means including a sleeve 226 on spool 217 backed up by spring227 tending to close annular passage 212a in much the same manner thatsleeves 218 and 218a tend to close annular passages 221 and 221a whenspools 217 and 211 are in their neutral positions. This arrangementprovides pressure sequencing to assure that pressure is always availableto release the steering clutch 6 regardless of the subsequent variablerequirements for brake control. Specifically, pressure in lines 89, 90may be depleted without similar depletion of fluid pressure that isavailable from pump 40 for control of steering clutches 5 and 6. Theimportance of this is evident during several operational maneuvers ofthe tractor, such as when manually applying one or both brakes 7 and 8when accompanied by the release of one or both steering clutches 5 and6.

Fluid pressure from the flow divider 46 supplied to main outlet port A,to chamber 210, through annular passage 212, chamber 213, passage 214,through check valve 215 and into chamber 216 is reduced as a result ofspool 217 movement downward. This movement causes spring 219 to reducethe force on sleeve 218 thereby permitting fluid from chamber 216 toflow through annular passage 221 and chamber 222 through outlet port Gto the tank 112 at progressively lower pressure in proportion to thespool travel. This action causes pressure in the right hand brakecylinder 10 to decay and allows the spring 27 in this cylinder 10 toapply the right hand brake 8.

A vehicle turn to the left is accomplished by pulling on the left handsteering lever 31 thereby moving valve spool 211 away from the stop 224awith the result that, in a like manner with relation to like components,pressure delivered from pressure port C will release the left handsteering clutch 5 and pressure reduction at port F will automaticallyallow the spring to apply the left hand brake 7.

Check valves 215 and 215a are required to prevent pressure feedback(pressure loss) from the brake cylinders 9 and 10 when the spools 211and 217 are starting to apply pressure to disengage the steeringclutches 5 and 6.

The pedal actuated supplemental brake control valve 43 serves to enableselective application of either or both brakes 7 and 8 in response todepression of single pedal 33 and also serves to automatically apply thebrakes 7 and 8 when the tractor transmission 4 is operating in neutraland fluid pressure in the transmission drops below some predeterminedvalue. Value 43 comprises a housing 100 having an axial bore 101 thereinin which a valve spool 102 is slideably mounted. Spool 102 is biasedtoward the right (referring to FIG. 1) by a compression spring 103 inchamber 99 which acts in combination with transmission fluid pilotpressure supplied to a port 104 through a supply line 105 from tractortransmission 4. Rightward movement of spool 102 operates to close anannular fluid passage 106 in valve 43 communicating between chambers 107and 108 in valve 43. Chamber 107 has a port 109 by means of which itcommunicates through a fluid line 95 with port 58 in shuttle valve 42.Chamber 108 has a port 110 by means of which it communicates through afluid line 111 to reservoir 112. Valve 43 comprises another passage 113having a port 114 by means of which fluid leakage from line 105 thatpasses spool 102 may be returned through a line 115 to a reservoir 116for the transmission fluid. Valve 43 also comprises an axially movablerod 120 which is connected by a linkage 121 to brake pedal 33 and hasits innermost end in abutting engagement with the end of valve spool102. Valve spool 102 is provided with a groove 123 which is in registrywith the passage 113 in valve 43. When both control levers 31 and 32 arein neutral position, both brakes 7 and 8 will be applied if either (1)the single foot brake pedal 33 is depressed, or (2) the transmission 4is shifted to neutral thereby reducing the pilot pressure in line 105.In either event pressure fluid in chamber 107 escapes at a lowerpressure through passage 106 to chamber 108 and to reservoir 112.Chamber 107 communicates with port 58 in shuttle valve 42. Fluidpressure from transmission hydraulic circuit line 105 acts on piston orspool 102 to urge poppet valve passage 106 closed. Spring 103 serves toachieve a proper balance between the transmission pilot pressure actingon spool 102 and the brake control pressure in line 95 so that whentransmission pilot pressure in transmission 4 and line 105 drops below apredetermined value, such as during a change in vehicle direction duringshift, the poppet valve passage 106 is permitted to open and release thepressure in line 95 to reservoir 112 and in brake actuators 9 and 10,thus allowing the brake springs 27 and 28 to apply brakes 7 and 8.

Shuttle valve 42 comprises a housing 70 having a bore 71 therein inwhich a shuttle valve spool 72 is slideably mounted and normallymaintained in centered position by compression type centering springs 73and 74 located in pilot pressure chambers 75 and 76 in the bore anddisposed between the spool ends and the ends of the housing. Valve spool72 is provided with a pair of spaced apart grooves 77 and 78 which arealigned or register with fluid flow passages 79 and 80, respectively,when the spool is centered. The passages 79 and 80, each of whichcommunicates with fluid inlet port 58, also communicate with the fluidports 81 and 82, respectively, which are connected by fluid lines 83 and84, respectively, to the ports 30 of the brake actuators 9 and 10. Thepilot pressure chambers 75 and 76 of shuttle valve 42 are connected bypassages 91 and 92, respectively, to the lines 83 and 84, respectively.When shuttle valve 42 is in neutral position, fluid from lines 83 and 84is combined and directed through passages 79 and 80, respectively, toport 58. Chamber 107 in valve 43 communicates with a " Y" passage 79, 80in shuttle valve 42 shown in FIG. 1. Lines 83 and 84 are branches oflines 89 and 90, respectively, leading from pressure ports F and E,respectively, of valve 41 to the left hand and right hand brakecylinders 9 and 10, respectively, and communicate with the passages 79and 80, respectively. Branch passages 91 and 92 from lines 83 and 84 aredirected to the pilot chambers 75 and 76, respectively, of valve 42 andact on spool 72 so that it will move to the right or left in response toa difference in pressure in lines 83 and 84. This action is such as toisolate the one of these passages 91 or 92 with the highest pressurefrom the other passages 91 or 92 and from action resulting from theoperation of supplemental brake control valve 43.

Valve 43 acting in conjunction with shuttle valve 42 then provides forsupplemental control of the automatic operation of the brakes 7 and 8 inresponse to operation of the left and right steering levers 31 and 32and also provides for automatic braking in neutral. The degree by whichautomatic braking is coordinated with steering control depends on thedesigned force and rate of springs 219 and 219a in valve 41.

Manual application of the brakes 7 and 8 is accomplished by depressingthe single brake pedal 33 thereby moving valve spool 102 of valve 43 tothe left in the drawing against spring 103. This allows fluid to passthrough line 95 into chamber 107, through passage 106 at modulatinglycontrolled pressure, to chamber 108 and then to sump 112. Fluid in line95 normally communicates with both brake actuator cylinders 9 and 10 bymeans of the dual passages 79 and 80 in shuttle valve 42.

If both control levers 31 and 32 are moved from neutral simultaneously,fluid pressure in both lines 83 and 84 acts on opposite ends of theshuttle valve spool 72. Equalization springs 73 and 74 at both ends ofspool 72, along with the equal pilot fluid pressure in the chambers 75and 76, retain the spool in a neutral position. This allows fluid inboth brake actuators 9 and 10 to escape to sump 112 and results inapplication of both brakes 7 and 8.

If only one control lever 31 or 32 is moved from neutral, then the fluidpressure being used to release the one brake acts on one end of theshuttle valve spool 72 to shift it in a direction to block one of thepassages 79 or 80 so that fluid from only one brake actuator 9 or 10 isallowed to escape to sump 112 to effect brake application.

I claim:
 1. In a hydraulic control valve:a housing having a pair ofbores therein; a pair of independently actuatable valve spools, one foreach bore, in said housing, each valve spool having a land thereon andbeing biased into a neutral position and selectively movable therefromto other positions; a pair of main inlet ports, one for each bore; twopairs of pressure ports, each pair of pressure ports including a firstand a second pressure port associated with one bore; and a pair ofpassages, each passage communicating between the main inlet port of onebore and the second pressure port of the other bore; a main outlet portin said housing connected to the second pressure ports of both bores;each valve spool when in neutral having its land interposed between themain inlet port and the first pressure port of its associated borethereby preventing communication therebetween; each valve spool whenmoved from neutral to another position decreasing communication to itsassociated second pressure port and moving the land interposed betweenthe main inlet port and the first pressure port thereby enablingcommunication between its associated main inlet port and its associatedfirst pressure port.
 2. A control valve according to claim 1 includingfirst pressure regulating means for each valve spool and responsive tovalve spool position and to fluid pressure at its associated secondpressure port for controlling communication between said second pressureport and said main outlet port.
 3. A control valve according to claim 1including second pressure regulating means for each valve spool andresponsive to valve spool position for controlling communication betweenits associated main inlet port and the second pressure port of the otherbore.
 4. A control valve according to claim 1 including check valves insaid passages to prevent back flow from said second pressure port.
 5. Ina hydraulic control valve:a housing having a pair of bores therein; apair of independently actuatable valve spools, one for each bore, insaid housing, each valve spool having a land thereon and being biasedinto a neutral position and selectively movable therefrom to otherpositions; a pair of main inlet ports, one for each bore; two pairs ofpressure ports, each pair of pressure ports including a first and secondpressure port associated with one bore; a pair of passages, each passagecommunicating between the main inlet port of one bore and the secondpressure port of the other bore; a main outlet port in said housingconnected to the second pressure ports of both bores; each valve spoolwhen in neutral having its land interposed between the main inlet portand the first pressure port of its associated bore thereby preventingcommunication therebetween; each valve spool when moved from neutral toanother position decreasing communication to its associated secondpressure port and moving the land interposed between the main inlet portand the first pressure port thereby enabling communication between itsassociated main inlet port and its associated first pressure port; firstpressure regulating means for each valve spool and responsive to valvespool position and to fluid pressure at its associated second pressureport for controlling communication between said second pressure port andsaid main outlet port; second pressure regulating means for each valvespool and responsive to valve spool position for controllingcommunication between its associated main inlet port and the secondpressure port of the other bore; and check valves in said passages toprevent back flow from said second pressure port.
 6. In a hydrauliccontrol valve:a housing having first and second bores therein; first andsecond selectively operable valve spools, one for each bore, in saidhousing, each spool having a land thereon and movable between a neutralposition and other positions; means for biasing said valve spools intosaid neutral position; a main fluid inlet port; first and second inletports, one for each bore, for receiving fluid from said main inlet port;a flow divider for supplying fluid from said main inlet port to saidfirst and second inlet ports; a first pair of pressure ports including afirst and second pressure port in said housing associated with saidfirst bore; a second pair of pressure ports including a first and secondpressure port in said housing associated with said second bore; a firstpassage in said housing communicating between said first inlet port andsaid second pressure port of said second pair of pressure ports; and asecond passage in said housing communicating between said second inletport and said second pressure port of said first pair of pressure ports;a main fluid outlet port in said housing connected to the secondpressure ports of both bores; said valve spools operating so that: whenboth are in neutral position, said first inlet port is in communicationthrough said first passage with said second pressure port of said secondpair of pressure ports while said first pressure port of said secondpair of pressure ports is maintained closed by the land of said secondvalve spool and said second inlet port is in communication through saidsecond passage with said second pressure port of said first pair ofpressure ports while said first pressure port of said first pair ofpressure ports is maintained closed by the land of said first valvespool; and when either or both of said valve spools are moved fromneutral, the pair of pressure ports associated with the valve spoolwhich is moved assume a condition wherein the second pressure portassociated therewith closes and the first pressure port associatedtherewith opens.
 7. A control valve according to claim 6 including apair of spring biased pressure regulating members on each valve spool,one member on its associated valve spool controlling communicationbetween the second pressure port of the pair of pressure ports of thatvalve spool and said main fluid outlet port, the other member on itsassociated valve spool controlling communication between its associatedinlet port and the passage connected to the second pressure port of thepair of pressure ports for the other bore, said one pressure regulatingmember being responsive to valve spool position and operating toincrease communication to ensure that there is enough fluid pressure ata first pressure port as the fluid pressure at a second pressure portdecreases.
 8. A control valve according to claim 7 including checkvalves in said first and second passages to prevent back flow from thesaid second pressure ports.